The invention relates to a drilling machine, in particular a hand-held core drilling machine, to a drilling machine-tool combination and to the use of such a drilling machine.
Core drilling is well known. In core drilling, a core drill, also called a drill bit, machines a substantially annular groove around a drilling core of a material to be drilled. In particular in the case of large drilling diameters and drilling depths, core drilling is particularly productive, since not all of the drilling cross section has to be machined. Core drilling is generally used widely in the building industry, for instance for drilling perforations in masonry, concrete or rock.
In order to drill in particular large core holes, core drilling appliances or core drilling machines are coupled usually to a stand or framework which is fixed to the work-piece. Such a drilling stand is intended to ensure sufficient guidance during the drilling operation and can furthermore be provided with manual or motor-driven feed drives. In addition, the drilling stands can absorb or support a counter-torque that is produced during drilling, said counter-torque being in the opposite direction to the drive torque. Thus, the burden on an operator can be significantly relieved and the risk of the core drill becoming jammed can be reduced considerably.
A disadvantage with stand-bound core drilling machines is the high time requirement for fastening and for setting up the stand. Thus, it is possible for instance for stands to have to be fixed to the masonry by way of a plurality of screw connections, which in turn have to be pre-drilled manually.
In order to drill core holes, in particular core holes having comparatively small dimensions, core drilling appliances can furthermore be guided manually or held manually. In order to improve guidance during the drilling operation, there can be provided tools, in the case of which the drill bit for drilling the drilling core is coupled to a center drill for drilling a center hole or pilot hole. In this case, the center drill is usually offset towards a workpiece to be drilled compared with a core drill bit, and so its tip can penetrate the workpiece alone at the start of the drilling operation without there being any significant engagement of the drill bit with the workpiece. The diameter of the center drill is in this case smaller than the diameter of the drill bit. In this way, although two concentric holes are introduced into the workpiece, the center drilling operation is tolerated for improving guidance in the case of hand-held core drilling.
A core drilling machine is known for instance from DE 10 2009 040 513 A1. This is a core drilling machine having a hollow drilling shaft which can be set into rotation by a drive unit. The core drilling machine is furthermore designed to hold a drill bit and a center drill. It has been shown that the center drill can improve the guidance of the core drilling machine when a core hole is drilled with the drill bit.
Core drilling is used in metalworking, too. However, since core holes in metal usually have to be made with greater precision than for instance core holes in masonry, primarily core drilling appliances which are guided on drilling stands were initially used. In the case of metal workpieces, such stands can be fixed for instance by magnetic force or by means of negative pressure. In addition, more recently, applications for hand-held core drilling in metal have been realized. In this case, particular requirements are imposed on the centring of the drill bit in order to prevent the drill bit from “running away”. A “run away” hole results in an increased tendency for the tool to jam or even break. Moreover, the probability of the resulting hole not being able to be used increases, since it does not satisfy the necessary accuracy.